A converter is a processing circuit that converts an input voltage or current source waveform into a specified output voltage or current waveform. A buck-derived switching converter (also referred to as a “buck converter”) is a frequently employed converter that converts a direct current (DC) input waveform to a specified DC output waveform. A characteristic of buck converters, in general, is that the DC output waveform is less than the DC input waveform. A buck converter that does not employ a transformer as an isolation stage is referred to as a non-isolated buck converter. The non-isolated buck converter typically includes switching circuitry coupled to an input source of electrical power. The switching circuitry includes at least one active switch. The switching circuitry is coupled to an output inductor and output capacitor which provides the DC output waveform (i.e., an output voltage) at an output of the non-isolated buck converter.
Multiple output switching converters are often employed to provide multiple output voltage levels driving independent loads at varying current levels. In some cases, the output voltage levels may be reversed in polarity (e.g., +12 volts and −12 volts) and referenced to a common return. With regard to switching converters that include an isolation stage, the multiple output voltages may be provided via multiple windings on the secondary side of a transformer. In non-isolated switching converters (e.g., non-isolated buck converters), however, deriving multiple output voltages, irrespective of the level and polarity of the voltages, is more complex to implement and may impact the overall efficiency of the switching converters.
Presently, a second output voltage may be derived from a multiple output non-isolated buck converter via an inductor. Under such circumstances, the second output voltage is rectified through a rectifier (e.g., a diode rectifier or synchronous rectifier) and post regulated to deliver the second output voltage at an auxiliary output of the multiple output non-isolated buck converter. While employing yet another technique, a second output voltage may be derived from a multiple output non-isolated buck converter by employing a charge pump therein.
While the aforementioned techniques have proven beneficial, the approaches suffer from the foregoing limitations. The technique of using the inductor for the purpose of providing multiple output voltages in the multiple output non-isolated buck converter typically employs either a peak charge rectified or forward rectified outputs that may suffer from significant ripple currents associated with the primary and auxiliary outputs of the converter. Even for smaller currents, series damping is generally a prerequisite, along with a large inductor to account for the peak currents and ripple condition associated with the primary and auxiliary outputs of the converter. Thus, the design generally calls for larger magnetic components within the multiple output non-isolated buck converter. Charge pumps, on the other hand, have restrictions on current outputs relative to the respective footprints. Therefore, the present techniques and methods of generating the second output voltage still call for larger surface area magnetic devices.
Accordingly, what is needed in the art is a circuit and method that maintains regulation of the output voltages for a multiple output converter such as a multiple output non-isolated buck converter, while preserving the overall efficiency of the converter.